Prior to the past several decades, scientists generally believed that it was impossible to restore hearing to the profoundly deaf. However, scientists have had increasing success in restoring normal hearing to the deaf through electrical stimulation of the auditory nerve. The initial attempts to restore hearing were not very successful, as patients were unable to understand speech. However, as scientists developed different techniques for delivering electrical stimuli to the auditory nerve, the auditory sensations elicited by electrical stimulation gradually came closer to sounding more like normal speech. The electrical stimulation is implemented through a prosthetic device, known as a cochlear implant (CI), which is implanted in the inner ear to restore partial hearing.
Cochlear implants generally employ an electrode array that is inserted into the cochlear duct. One or more electrodes of the array selectively stimulate the auditory nerve along different places in the cochlea based on the frequency of a received acoustic signal picked up by a microphone and transformed to an electrical signal by a digital signal processor (DSP) unit located in the external ear piece of a cochlear implant front end.
After a patient has been provided with a CI, it is necessary to initially “fit” or “adjust” the device during a fitting session. As used herein, it should be noted that terms “fit”, “adjust”, “fitting”, “adjusting”, “program”, or “programming” relate to making electronic or software programming changes to the CI device. A proper fitting is essential to ensuring the CI user experience natural sound quality. Currently, the fitting session suffers from inefficiency and subjectivity for a few reasons. Because a new CI user is used to experiencing either poor sound quality or no sound at all, he/she finds it difficult to qualitatively communicate a perceived sound quality and preference to a technician during the fitting session. This results in a fitted device not accurately tailored to the specific CI user. Worst yet, younger CI users (i.e. children) are incapable of communicating effectively the nature of experienced sound quality to the technician.
Characteristics of a cochlear implant front's end play an important role in the perceived sound quality (and hence speech recognition or music appreciation) experienced by the CI user. These characteristics are governed by the components of the front-end comprising a microphone, an ND converter, and the acoustic effects resulting from a location of the microphone on the user's head. While the component characteristics meet pre-defined standards, and can hence be compensated for, the acoustic characteristics are unique to the CI user's anatomy and his/her placement of the microphone on their head. Specifically, the unique shaping of the user's ears and head geometry can result in substantial shaping of the acoustic waveform picked up by the microphone. Because this shaping is unique to the CI user and his/her microphone placement, it cannot be compensated for with a generalized solution. This issue can be even more critical in beamforming applications where signals from multiple microphones are combined to achieve a desired directivity. It is critical for the multiple microphones in these applications to have matched responses. Any differences in the microphones' responses due to their placement on the patient's head can make this challenging.